The present invention relates to phased array antennas, and more particularly, to multi-frequency band phased array antennas employing a coplanar dipole array having multiple feed ports.
Heretofore, shipboard radars, airborne radars, and ground based radars have generally employed separate radar antennas for different radar operations. For example, a radar might employ a first antenna for surveillance, a second antenna for communications, and a third antenna for ESM applications. However, the disadvantage of separated radar antennas is that the radar is not compact. Instead, it is heavy, unwieldy and has little mobility. To overcome this disadvantage, it has been found desirable to have a multi-frequency band phased array antenna.
One prior art attempt to supply this need is described in a paper entitled "Experimental Results of a Multi-Frequency Array Antenna" by J. E. Boyns and J. H. Provencher, published in the IEEE Transactions on Antennas and Propagation, January 1972, pages 106, 107. It describes an array antenna containing three arrays of interlaced radiating elements with operating frequencies in L, S and C bands. The array elements are open-ended waveguides. However, that multi-frequency array has several disadvantages. The presence of the low frequency elements generates significant grating lobes due to the scattering of the high frequency signals from the low frequency elements. The radiating elements for different frequency bands are cross-polarized, which limits system applications. Furthermore, the high frequency incident signal is coupled into the low frequency array and the isolation is not good. This is discussed in the above-cited paper.
Accordingly, it is a feature of the present invention to provide an arrangement of radiating elements combined into arrays for multiple frequency phased arrays that span over several frequency bands. Another feature of the invention is the provision of a multi-frequency band phased array antenna that has a compact radiating aperture design with no blockage between radiating elements. Yet another feature of the present invention is to provide a multi-frequency band phased array antenna that is compact, light in weight and mobile.